I was asked to explain the following periodic trends:

- diagonal relationships
- knight's move relationships
- actinoid relationships
- lanthanoid relationships
- combo elements
- pseudo elements

I do know that the diagonal relationship between elements are between lithium/magnesium, beryllium/aluminum, and boron/silicon and that these elements are similar in their charge density.

For the knight's move, the elements have similar oxidation states such as copper/indium, indium/bismuth, silver/thallium, cadmium/lead, zinc/tin, and gallium/antimony.

I am a bit confused on whether the lanthanoid and actinoid relationships are the same as referring to the lanthanide and actinide series. If so, what relationship do they have?

I was able to find that the combo elements are boron and nitrogen but I am not sure why.

I was also able to find out that the pseudo elements are ammonium and cyanide but I am not sure why and if my answer is correct.

I tired to look for the explanation but I could not find it. It's not in any of my inorganic chemistry books either. Help would be very much appreciated. Thank you.